Electrical transport mechanism and magnetoresistive behavior of trilayer La0.7Sr0.3MnO3/γ-Fe2O3/La0.7Sr0.3MnO3 (FM/FIM/FM) manganites

Abstract

The magnetization, electrical transport, and magnetoresistance (MR) behavior of Pulsed Laser Deposited polycrystalline tri-layer La0.7Sr0.3MnO3 (LSMO)/γ-Fe2O3/LSMO film and single layer LSMO film on Si (100) substrates are investigated in the temperature range of 5 K–300 K. A magnetic anomaly appears in the magnetization {M(T)} and resistivity {ρ(T)} characterizations of the trilayer film at around 100 K, which is quite robust and is present even at 7 T of the applied magnetic field. The trilayer sample exhibits metal to insulator (MIT) transition at 210 K. The transport behavior of both the films is analysed in the context of nearest-neighbour small polaron hopping model (SPH), Mott variable range hopping (VRH) mechanism as well as thermal activation (TA) model in different temperature ranges for both the films under study. The correlated polarons or less mobile bipolarons exist in the metallic regime of the trilayer sample due to the presence of magnetic inhomogeneities. The low temperature resistivity upturn is observed in LSMO film, which is attributed to the spin fluctuations (Mn3+–O–Mn4+) due to thermal energy. The trilayer sample exhibits a large negative MR of (∼45%) at low temperature (5 K). It manifests consistent negative CMR effect across the whole temperature range of 5 K–210 K (MIT). The improved MR behavior of the trilayer sample as compared to the LSMO film is due to enhanced polycrystalline character of the trilayer film owing to higher grain boundary density and spin dependent scattering at both the interfaces of LSMO/γ-Fe2O3/LSMO structure.